1. Field of the Invention
The present invention relates to electric generators for use in various types of electronic apparatuses, such as watches, hearing aids, cellular phones, or personal computers.
2. Background Art
In recent years, there has been advancement of diversification and functionality of electronic apparatuses, such as cellular phones and personal computers. Along therewith, there have been increased processing loads exerted on control devices such as CPUs, thereby increasing electric power consumption and thus increasing the frequencies of recharges and battery replacements. Therefore, electronic apparatuses have been required to incorporate electric generators therein.
Such a conventional electric generator will be described with reference to FIG. 11. FIG. 11 is a schematic cross-sectional view of a conventional electric generator. Electric generator 10 includes movable electrode 1, swingable part 2, fixed electrodes 3, resistance element 4, electric-charge supply electrode 5, insulation part 6 and electron discharge portion 7.
Movable electrode 1 is formed of an electret. “Electret” refers to a material capable of continuously forming an electric field and can be fabricated by, for example, applying a DC voltage to a dielectric material such as a resin, under a high temperature, for charging it. Electrons have been preliminarily injected into movable electrode 1, so that an electric charge is held in a surface thereof.
Movable electrode 1 is provided on the lower surface of swingable part 2. Fixed electrodes 3 face movable electrode 1. Fixed electrodes 3 and swingable part 2 are connected to respective end portions of resistance element 4. Insulation part 6 is provided between the lower surfaces of fixed electrodes 3 and electric-charge supply electrode 5. Insulation part 6 is provided with a recess. Electron discharge portion 7 is provided on the bottom surface of the recess.
If vibrations are applied to electric generator 10 from the outside, swingable part 2 sways in the horizontal direction, which causes the projection of movable electrode 1 opposing to fixed electrodes 3 to intersect with fixed electrodes 3. Hereinafter, this state will be simply expressed as “movable electrode 1 intersects with fixed electrodes 3”. Electric charges are induced in fixed electrodes 3 intersecting with movable electrode 1, due to electrostatic induction. For example, when a negative electric charge is held in the surface of movable electrode 1 which is faced to fixed electrodes 3, positive electric charges are induced in fixed electrodes 3. As a result, a voltage is applied between the opposite ends of resistance element 4, thereby inducing an electric current in the downward direction.
By causing movable electrode 1 and fixed electrodes 3 to intersect with each other over larger areas thereof, a downward electric current flows through resistance element 4, as described above. On the other hand, if the areas of movable electrode 1 and fixed electrodes 3 which intersect with each other are decreased due to vibrations of swingable part 2, an upward electric current flows through resistance element 4, since the positive electric charges induced in fixed electrodes 3 are decreased. In other words, since movable electrode 1 vibrates while intersecting with fixed electrodes 3, a downward or upward electric current flows through resistance element 4, thereby inducing an AC voltage between the opposite ends of resistance element 4.
Further, electron discharge portion 7 is provided, in order to generate a voltage between the opposite ends of resistance element 4, even when movable electrode 1 has no portion intersecting with fixed electrodes 3. Electron discharge portion 7 discharges electrons from the surface of electric-charge supply electrode 5 for injecting electrons into movable electrode 1 provided oppositely thereto when a voltage is applied between fixed electrodes 3 and electric-charge supply electrode 5. Thus, in the event of a drop of the voltage between the ends of resistance element 4, a voltage is applied between fixed electrodes 3 and electric-charge supply electrode 5, thereby preventing the drop of the voltage induced between the ends of resistance element 4.
Electric generator 10 having the aforementioned structure is formed on a circuit board (not illustrated) in an electronic apparatus (not illustrated) for supplying electric power for driving the electronic apparatus, even when the electronic apparatus incorporates no battery.
However, since electric generator 10 is formed on the circuit board in the electronic apparatus, only the electronic apparatus structured on the presumption that it is incorporated with electric generator 10 is enabled to use electric generator 10 for electric power generation.